The present invention relates to transmission systems and more particularly to a continuously variable transmission system.
Most mechanical power sources operate most efficiently if tailored to operate in narrow speed ranges. For example, a gasoline engine typically runs between 1,000 and 5,000 RPM (revolutions per minute) and only operates at peak efficiency in a much narrower band. To power an motor vehicle this must be translated into a wheel speed ranging from 0 to 1,000 RPM (high limit depends on wheel size and top speed). There are at present three ways this is commercially accomplished. The first is a "manual" transmission which has now up to 7 speed ranges, with which to divide the overall range into and a clutch to shift between the ranges. The second type is an "automatic" transmission which has up to 3 ranges like a "manual" transmission plus a hydrokinetic clutch which helps it between ranges. The third type is called a "ECVT" transmission standing for electrically controlled variable transmission. This is an option for only one motor vehicle, the Subaru Justy. The ECVT transmission is a modification of an arrangement of two coaxial cones with the small diameters thereof facing one another.
The employment of cones in transmission systems is well known as evidenced by the following U.S. Pat. Nos. 657,855; 1,048,220; 1,256,418; 1,358,447; 2,705,892; 3,021,717; 3,257,857; 3,894,439 and 3,906,809.
The prior art use of cones in a transmission system have cones that are very short for their width and a V-belt that rides between them. The tension on the belt causes the belt to act or be acted upon by the cones through friction. By pressing the cones together the belt is caused to slide outward away from the axis of rotation. This is a workable system as evidenced by the fact that it is used in a moped sold by Motobecane. The problem with this design is that the belt is overworked tensionally and frictionally. To provide driving force the belt must be in tension which is added to the tension that the belt must sustain due to driving forces. Frictionally, the belt must be sticky enough for the cones to grip to provide driving force, yet must still be able to slide to change gearing ratios.
A modification of the above prior art arrangement was to replace the V-belt with a large number of trapezoidal (the true cross-section of a V-belt) metal plates with a cord running through their centers. The frictional contact is now metal to metal, and the driving force is now the plates pushing on one another. This in effect separates the two jobs the belt had to accomplish, that of tension and that of driving force. This type of transmission system has been viewed favorably except that it is only offered as an option with small engines and without four-wheel drive. One of the problems with this type of transmission system is handling high torque applications.
An answer to the above problems is to eliminate the need for belt tension to provide frictional driving force and eliminate the need for the two pieces that hold onto one another to also be able to slide against one another. If this is achieved then high torque applications will be possible because frictional pressures can be increased. Whatever the precise merits, features and advantages of the above cited prior art, none of them achieves or fulfills the smooth change of ratios under high torque, without the excessive loss of energy which the invention of the present application overcomes.